1. Field of the Invention
This invention relates to an ultrasonic vibrator for a vibration type motor including a member, for example, a rotor, which is in pressure contact with a vibration member. The rotor and the vibration member are moved relative to each other by a vibration generated in a vibration generating element, the vibration member being vibrated by the vibration of the vibration generating element. More particularly, the present invention relates to a vibrator for a pencil-like motor (hereinafter referred to as the pencil-type motor).
2. Related Background Art
There has recently been proposed a vibrator in which two vibration generating elements such as piezo-electric elements are superposed one upon, the other and, electrically conductive metal blocks for receiving such vibration are provided above and below the vibration generating to elements the upper and lower blocks being fastened by fasteners such as electrically conductive bolts, whereby the two vibration generating elements are held between the blocks.
In such a vibrator, a sensor including, for example, a piezo-electric element for detecting the vibration state of the vibration, is provided between the aforementioned vibration generating elements and the upper or lower metal block, with two sensors being required.
A vibrator according to the prior art will now be described briefly with reference to FIG. 3 of the accompanying drawings.
A vibration generating element including piezo-electric elements 7-13 polarized in the direction of thickness is provided between electrically conductive metal blocks 1 and 3, and an AC voltage is applied to the piezo-electric elements 7 and 9 constituting phase A through earth electrodes 19, 23 and an electrode 21 for phase A, while an AC voltage electrically having a phase difference of 90.degree. with respect to said AC voltage is applied to the piezo-electric elements 11 and 13 constituting phase B through earth electrodes 23, 27 and an electrode 25 for phase B.
Two sensors for detecting the vibration state which comprise, for example, piezo-electric elements 15 and 17 are provided between the earth electrode 27 and the lower metal block 3, and an electrical signal corresponding to the rotational (elliptical) vibration state of the upper and lower metal blocks can be detected between an electrode 29 and the earth electrode 27 held between the two sensors 15 and 17. In the case of this prior-art ultrasonic vibrator, at least two sensors for vibration detection are necessary as shown in FIG. 3.
This is because assuming, for example, that the lower sensor 17 is absent, electrode 29 will assume the same potential as earth electrode 27, which contacts the lower metal block 3. Lower metal block 3 has earth potential because it is electrically connected to metal block 1 of earth potential through a bolt 5. Accordingly an electrical signal produced in the sensor 15 could not be detected between output terminals 27A and 29A.
Alternatively assuming that sensor 15 is absent, electrodes 27 and 29 would be short-circuited and an output signal of sensor 17 could not be detected between the output terminals 27A and 29A. On the other hand, if in the state in which sensor 15 has been eliminated, electrode 29 is brought into contact with the lower metal block 3, so that the aforementioned short-circuited state may not be brought about and the sensor 17 is held by and between the electrodes 27 and 29, electrodes 27 and 29 will assume the same potential for a reason similar to that in the case where the sensor 17 is absent and therefore, the output signal of the sensor 17 could not be detected.
As noted above, in the case of the prior-art vibrator, there has been the disadvantage that at least two sensors are required and the vibrator becomes expensive.